Contemporary plastics are typically comprised of one or more base polymers or resins, one or more colorants or colorant additives, and other additives. Such additives may include, for example, fiberglass for structural reinforcement, flame retardants, plasticizers, or mold release agents. The plastics are manufactured by mixing these constituents, usually by machine, to form a substantially homogeneous polymer mixture. In this context, a substantially homogeneous compounded polymer mixture is distinguished from a polymer mixture having a substantially uniform color. In addition to the heat produced by mixing these constituents, termed "shear heat," other external heat may also be supplied. The resulting material, frequently produced in the form of strands, webs, bars, sheets or films, to name only a few possible shapes, may, after at least partial solidification of the mixture, then be pelletized to produce a final polymer product.
Experience has shown that the color of the resulting polymer product may depend upon several factors. These include, among others, the concentration and type of colorants, the base resins employed and their concentration by weight, the temperature history during mixing, and the ultimate degree of constituent inter-mixing achieved during processing. Thus, variations in color between polymer products may arise for a large variety of reasons. For example, color may vary among products due to polymer product formulation or recipe differences. Likewise, color variations may exist between lots for a given product formulation or recipe due to, for example, machine-to-machine differences. Furthermore, color differences may exist within lots due to changing raw material characteristics, changing operating conditions, and inaccuracies and other anomalies in processing, such as differences in the constituent feed rates. Thus, a need exists for a reliable and effective means or method of controlling the color of compounded polymer(s) while the compounded polymer(s) are in-process and, thus, bringing a production lot of the compounded polymer(s) to the desired color and substantially maintaining that color throughout the production run.